In the automobile industry it is common to operate various vehicle accessories, such as the power steering pump, oil and air pumps, air conditioning and alternator, by a single endless belt driven by a pulley connected to the engine crankshaft. This system is referred to as a serpentine drive belt system. To ensure optimum operating efficiency for these various accessories, it is necessary that the drive belt be maintained at a predetermined tension to assure efficient performance of the accessories as well as satisfactory service life for the belt. Due to the relatively greater length for the single drive belt which replaces a plurality of smaller belts, there is a greater tendency for the belt to stretch which will affect the operating characteristics of the driven accessories. Therefore, it is desirable that a belt tensioning device be used for these endless belts to provide reliable service over an extended period of time and to maintain a constant amount of tension thereon regardless of the amount of belt stretch.
Numerous devices have been proposed and used to accomplish this purpose. One type of tensioner uses a bushing formed of an elastomeric material which is placed in compression by some mechanical means for continuously exerting a tensioning force on the belt. These tensioner constructions, which use an elastomeric material, have the disadvantages in that the high load rate which they exert on the belt results in the rapid loss of tensioning as the belt stretches, and this load rate limits the stroke of the belt-engaged idler pulley to a shorter distance than desired. Also, sudden acceleration and deceleration of the drive belt can cause a whipping action to occur which creates a time lag before full damping is achieved.
Other types of tensioning devices and arrangements are provided with some type of mechanical retaining means which limits the movement of the belt tensioning member in an opposite nontensioning direction, thereby maintaining a constant tensioning force on the endless drive belt and eliminating the undesirable effects of belt whipping.
Representative of the art is U.S. Pat. No. 4,392,840 (1983) to Radocaj which discloses a device which maintains a predetermined tensioning force on the endless drive belt for vehicle accessories by use of a one-way clutch which prevents return of the tensioning means from its forward most tensioning position. In the preferred embodiment, a cylindrical shaft is mounted in a fixed position adjacent the drive belt. A roller clutch assembly is mounted on the shaft and includes an outer clutch housing rotatably mounted on the shaft. An outwardly extending lever is attached to the clutch housing and has an idler pulley rotatably mounted on the extended end of the lever. The pulley is moved into tensioning engagement with the drive belt by a torsional spring which is telescopically mounted on the shaft and clutch housing. The spring moves the pulley in a belt tensioning direction. The one-way clutch assembly preferably includes a roller clutch which consists of a plurality of rollers which are interposed between and are biased by a plurality of leaf springs into a wedging relationship with the shaft surface and ramps formed on a bearing cup. The rollers permit free movement of the clutch housing and attached lever in the belt tensioning direction while preventing movement of these components and associated idler pulley in the opposite nontensioning direction because of the wedging action of the rollers.
What is needed is a tensioner comprising a first damping member wedgingly engagable between a pivot arm and a second damping member. The present invention meets this need.